ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
641 
meristem of tlie root the periblem arises from two initial layers. There 
is no pericycle in the upper part of the hypocotyl or in the stem. The 
xylem-bundles of the root are perfectly continuous with those in the 
stem ; the passage from the centripetal to the centrifugal arrangement 
takes place without torsion. The fibres of the hemp are always more or 
less fusiform, and have often spathulate, curved or wart-like ends, but 
are never branched. 
Wood of Pomese.* — Dr. A. Burgerstein has continued his investi- 
gations of the structure of the wood in several genera of this family. Ho 
states that, in the development of the histological elements of the secon- 
dary xylem, there is only a gradual differentiation, and that transitions 
occur in all directions. The medullary rays consist, with some excep- 
tions, of only one or two rows of cells, or partially of three. Several 
genera exhibit diagnostic characters in the structure of the wood. 
Absciss-layer in the Leaves of Monocotyledons.! — In the leaves of 
Narcissus , Galanthus, and Leucojum, Mr. J. Parkin has observed the 
formation of a layer of cells with corky walls which cause the detach- 
ment of the leaf from its tunicate base. Some time before the leaves 
turn yellow, certain of the parenchymatous cells situated a little above 
the tunicate base of the foliage-leaf become meristematic, and divide to 
form a zone of narrow cells with conspicuous nuclei and abundant 
protoplasm. 
Resin-galls of the Abietineae.! — Herr P. Nottberg discusses in 
detail the formation of masses of resin between the wood and bark in 
pine-stems. Their formation is always the result of the energy of the 
cambium in repairing an injury. Immediately after their formation the 
cells of this pathological parenchyme begin to form resin internally ; but 
whether the resinogenous layer arises from the cell-wall or from the 
protoplasm is uncertain. The resin-passages of the duramen are always 
closed by thyllae, thus preventing any external communication through 
injury to the alburnum. In the silver-fir ( Edeltanne ), which does not 
normally produce secretion-receptacles, resin-passages are formed as the 
result of injury. 
(4) Structure of Organs. 
Influence of Carbon dioxide on the Form and Structure of 
Plants.§ — M. E. C. Teodoresco compares the effect on the form and 
structure of plants ( Lupinus albus, Phaseolus multiflorus, Pisum sativum , 
Faba vulgaris) of an atmosphere containing a larger amount of carbon 
dioxide than ordinary atmosphere, with one deprived as far as possible 
of that gas. He finds that in the former case the plants have their 
hypocotyl or their first internodes shorter, but the following internodes 
longer, the total length of the stem being usually greater. As a rule, 
the internodes have in the former case a larger diameter, the number of 
vascular bundles being also often greater ; in each bundle the xylem, 
the phloem, and the generating zone (cambium), are also more fully 
* SB. k. Akad. Wiss. Wien, cvii. (1898) pp. 8-22. Cf. this Journal, 1897, p. 546. 
f Ann. of Bot., xii. (1898) pp. 151-3 (2 figs.). 
X Zeitschr. f. Pflanzenkrankheiten, vii. (1897) pp. 181 et seq. (1 pi. and figs.). 
See Bot. Centralbl., lxxv. (1898) p. 209. 
§ Comptes Bendus, cxxvii. (1898) pp. 335-8. 
2x2 
